There may be a planet at an enormous distance from the Sun: perhaps 200 AU (astronomical units, Sun-Earth distances) at perihelion, and 600 or even 1200 at aphelion. It would orbit the Sun in 15,000 or 20,000 years; its mass would be about 10 times that of Earth.
(For comparison, Jupiter’s and Neptune’s distances are 5 and 20 AU, their masses about 300 and 17 Earths.)
The announcement was made by Michael Brown and Konstantin Batygin, of Caltech, in the Astronomical Journal of Jan. 20. The evidence is a “clustering” of the orbits of six of the most remote among the known small bodies in the outer solar system; they have perihelia relatively close to each other and near the ecliptic (the general solar-system plane). This clustering was noticed in 2014 by Scott Sheppard and Chad Trujillo. Brown and Batygin spent months testing computer models, and the model offering the best explanation is that the smaller bodies have been “shepherded” by a large one in an orbit similarly tilted but with perihelion in the opposite direction. They say there is only a 0.007 percent chance of the clustering being merely coincidental. Other scientists are as excited as the discoverers, but some (such as David Jewitt, pioneer in the field) find it not yet statistically certain. It is a hypothesis, rather than a fact, until the planet is actually observed; which will be mighty difficult with the largest of telescopes, because its light would be some 10,000 times fainter than Pluto’s.
There have been Planet 9s or Planet Xs before A planet X was hypothesized because of discrepancies in the motion of Uranus, discovered, and named Neptune. Another was suspected, discovered, and named Pluto. Planets inward of Earth were “discovered” during eclipses of the Sun. Pluto was considered to be the ninth planet, from its discovery in 1930 till 2006, when it was demoted to “dwarf planet,” partly as a result of Michael Brown’s discovery of a more distant body of about Pluto’s size. A distant Jupiter-sized planet was suggested as the explanation for certain comets’ orbits. There is a recent disputed microwave observation of a planet 300 AU out.
Look at the second and longer for some accuracy and a diagram, and at the poor Independent for some hilarity. It used to be our favorite newspaper but may now be unable to afford copy-editing and fact-checking. “Brown” is referred to before he has been mentioned. Several times the planet is “sitting” out there; hardly an apposite word for a hunk of matter hurtling, even if at only about 2,000 miles an hour. The solar system is confused on the one hand with the set of major planets – it “doesn’t often change” and “went back to having eight members” – and, on the other hand, with the galaxy or the universe: the planet causes disturbances in “the far star system” or is “at the edge of the universe.” That gorgeous misstatement – rather like saying that your fingernail is on the Moon – seems to have been removed after some derisive comments. No comment on “So little light is sent back from that far away that it might never make it back for us to see” or “If the new planet is real, then it will definitely be a planet.”